The present invention relates to a structure of a liquid crystal display device (liquid crystal display panel) and a method of manufacturing the liquid crystal display device, and more particularly, to optimization of an arrangement of bead spacers forming a space between a pair of substrates included in the liquid crystal display device.
As shown in FIG. 9, a liquid crystal display panel (liquid crystal display device) 9 is constructed as described below, in which a liquid crystal layer 5 is sandwiched between a pair of (two) substrates typified by a thin film transistor (TFT) substrate 1a, on which thin film transistor is formed and a color filter (CF) substrate 1b on which red, blue, and green color filters 14R, 14G, and 14B are formed; the pair of substrates 1a and 1b are bonded to each other; and the circumferences of the respective substrates are surrounded with a sealing agent and are fixed to each other by bonding.
In the liquid crystal display panel 9, a gap g (hereinafter, referred to as cell gap) between the two substrates 1a and 1b, in which the liquid crystal 5 is sealed, is an important element that determines display quality. In particular, the absolute dimension of the cell gap g and uniformity of the cell gap g over the entire surface of the display area of the liquid crystal display panel 9 are important. Therefore, in the liquid crystal display panel 9 having the above-mentioned structure, in order to keep the gap between the two substrates constant, it is usual to disperse spacers 3 (hereinafter, referred to as bead spacers), which are spherical transparent particles made of glass or a synthetic resin whose grain size is uniform as shown in FIG. 9, between the two substrates to be used.
However, in the liquid crystal display panel having a system involving dispersing the bead spacers 3 on the substrate to be used, fabricating work is performed after dispersing the multiple bead spacers on the substrates. Due to this process, the bead spacers may spill from the substrate at the time of manufacture, which brings about contamination in a production line and becomes a cause of defective products. Moreover, in the liquid crystal display panel whose fabrication is completed, if the bead spacers are inserted into display pixels together with the liquid crystal, the bead spacers displace the liquid crystal. Accordingly, predetermined deflection of light does not occur in that portion, causing a display defect. For example, when the transparent particles are used in the liquid crystal display panel, and the liquid crystal display panel is set to a black display, only the bead spacer portions form luminescent spots.
Moreover, if the bead spacers are present in the display pixels, an arrangement of the liquid crystal molecules in the vicinity of the bead spacers is disturbed, generating light leakage in those portions. This phenomenon leads to occurrence of a problem in that contrast of the liquid crystal display panel is lowered and a detrimental influence is exerted on its display quality. In order to solve the problem, a method is proposed in which columnar spacers 3a (hereinafter referred to as photo-spacers) are provided between the pixel portions on a CF substrate 1b, as shown in FIG. 10 (between non-display areas 15 which separate a plurality of pixels 14, which are light shielding layer portions, hereinafter referred to as the BM portions).
Generally, the photo-spacer 3a is formed by the following methods:    (1) photosensitive resin that will act as a spacer is coated on a principal surface of the substrate by a spin coating method, a slit coating method, printing, or the like so that the photosensitive resin will be of a predetermined thickness;    (2) the photosensitive resin is dried;    (3) using a photomask so that a portion of the spacer has a convex form on the substrate, the photosensitive resin is exposed using an exposure light source through the photomask;    (4) the photosensitive resin is subjected to a developing process, and the photosensitive resin coated on any portion that is not intended to act as the spacer is removed; and    (5) developing solution adhered to the substrate is washed away, and the substrate is dried.
The photo-spacer formed by any of the above-mentioned methods can be arranged in arbitrary positions of the light shielding portion (black matrix, BM) 15 located between pixel portions that do not affect the display quality. As a result, any of the above mentioned methods can prevent lowering of the display quality caused by the light leakage from the photo-spacer portions that are a problem with the bead spacer.
However, in order to form the photo spacers described above on the substrate, the above-mentioned process is necessary, thereby increasing manufacturing cost. Besides, when the heights of the photo spacers are to be made equal to one another over the entire surface of the substrate, there are many technical problems.
Therefore, in recent years, the following technology has been studied. According to the technology, the bead spacers which are used up to now, equal in particle size to one another and made of a synthetic resin, are employed instead of the photo spacers. The bead spacers are not disposed over the substrate at random, but disposed in the light shielding portions which do not affect the display quality and are located between the pixel regions. In this case, an ink jet method or a printing method is used.
Because the bead spacers can be disposed at fixed points, a photolithography process required to form the photo spacers is omitted. Therefore, the photosensitive resin which is the material of the photo spacers and the developer and the cleaning solution which are required for developing processing are omitted, which not only leads to a reduction in cost, but also is effective in establishing a mass production technology that gives consideration to the environment and resources.
Findings with respect to the fixed point arrangement technique for the bead spacers and the fixing strength of the bead spacers are disclosed in Japanese Patent Laid-open Publication No. 2005-037721 (hereinafter, referred to as Patent Document 1), Japanese Patent Laid-open Publication No. 2005-004094 (hereinafter, referred to as Patent Document 2), Japanese Patent Laid-open Publication No. 2004-170537 (hereinafter, referred to as Patent Document 3), Japanese Patent Laid-open Publication No. 2004-037855 (hereinafter, referred to as Patent Document 4), and Japanese Patent Laid-open Publication No. 2006-053380 (hereinafter, referred to as Patent Document 5).
Materials and characteristics of an alignment film to which the bead spacers are disposed are disclosed in Japanese Patent Laid-open Publication No. H 11-228823 (hereinafter, referred to as Patent Document 6), Japanese Patent Laid-open Publication No. 2006-030961 (hereinafter, referred to as Patent Document 7), Japanese Patent Laid-open Publication No. 2005-275118 (hereinafter, referred to as Patent Document 8), Japanese Patent Laid-open Publication No. 2003-295195 (hereinafter, referred to as Patent Document 9), Japanese Patent Laid-open Publication No. 2006-017982 (hereinafter, referred to as Patent Document 10), Japanese Patent Laid-open Publication No. 2006-152247 (hereinafter, referred to as Patent Document 11), and Japanese Patent Laid-open Publication No. 2006-010995 (hereinafter, referred to as Patent Document 12).